Reciprocal support networks have become increasingly important in healing disaster wounds of adversely affected communities and improving their resilience. This paper demonstrates the empirical and credible evidence of social support network legacies and their characteristics and evolutionary patterns on flood disaster preparedness and recovery from flooding events, focusing on informal urban settlement areas of the city of Colombo, Sri Lanka. This study utilizes social network analysis measures such as degree density, closeness, and betweenness centralities for analyzing behaviors of reciprocal support networks. A key finding is revealed that social collaboration helps to revive urban informal livelihoods affected by the flood in effective ways. This study also demonstrates that the provision of information, activities such as evacuation, moving belongings from and to affected households, provision of food, water, and other basic needs including health supports, shelter, emotional supports, and cleaning contaminated households and public places have played a significant role in flood disaster preparedness vis-à-vis improving urban resiliency and recovery of urban informal livelihoods. In contrast, the involvements of flood disaster supportive network actors such as relatives, friends, neighbors, admin officials, and volunteers have been changed over the flood phases along with improving urban resilience.